Homebrew Galena Crystal Set

Enjoying a 1920's radio experience

Ever since my youth, I have been attracted to crystal radios I had seen pictured in old books. There is a special appeal about a device, however primitive, that can pull in radio voices and music through the air from many miles away without batteries or electrical power of any kind, just an antenna and a ground.

That explains my immediate attraction to this little homebrew crystal radio with galena detector found at a swap meet. It was built into a deep cigar box using a heavy paper roll as a coil form. The coil form measures 4 1/4 inches long with 3 3/4 inches outside diameter. The coil itself consists of 99 turns of solid double-cotton covered wire tapped every 9 turns. Those taps are fed to ten smooth-head screws that make up the tap selector switch contacts.

Repairs
As with all older electronics, the first repair is a good cleaning, making sure the solder joints are in good shape, and applying a bit of deoxit to all moving electrical contacts, in this case the ten-position tap switch and the crystal holder.
The top of the cigar box had been removed and apparently lost over the years. The cover had been fastened with a small nail which was still on the box. I made a top cover from another old cigar box lid.
The galena crystal was potted in Wood's metal that had separated into two pieces. Quick work with a soldering iron solved that problem. I cleaned the galena surface with rubbing alcohol as recommended in older articles. I then measured forward and back resistance ratios of the galena-and-cats-whisker diode. While there is a signifcant difference between forward and back resistance readings on an ohmmeter, the ratio was nowhere close to that of a modern germanium diode, thus limiting the efficiency of the crystal.

A 1920s experience
I hooked up the set to my 80 meter dipole antenna and listened to the two local AM stations with adequate volume using my equally old but very efficient Baldwin headphones. I could find sweet spots with the "cat's whisker" on the galena crystal that worked reasonably well. However, connecting a 1N34A germanium diode in series with the headphone lead to the galena crystal made a major difference. I could see why the introduction of fixed germanium diodes quickly ended the era of the galena and cat's whisker detector.

The ten-position tap switch enabled good separation in tuning of the two local stations which are 370 KHz apart. At night I was able to also comfortably listen to a some distant stations with strong signals.
I also tried a very long wire antenna but found the volume to be about the same as with the 80 meter dipole.
Living the experience of a 1920s listener was the fun part. My hat is off in tribute to the quality work of the unknown builder of this very nice little set.